CA2224634A1 - Prothrombin derivatives - Google Patents

Abstract

The invention relates to novel prothrombin mutants or derivatives thereof having one or more changes in the protein sequence as against the natural protein, are either inactive or have an activity of 10 % at the most and preferably no more than 0.25 % of the natural protein and have a bonding capacity to natural ligands (natural or artificial anticoagulants) essentially corresponding to that of the natural protein. The description also relates to the use of mutated prothrombin mutants or derivatives as pharmaceutical preparations.

Description

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Prothrombin Derivatives The invention relates to new prothrombin mutants or derivatives thereof which may be utilized as antagonists of their natural functions.
The mechanism of blood coagulation normally occurs in a cascade of two possible routes. One of the routes, the so-called extrinsic blood coagulation, starts with the liberation of thromboplastin and the activation of factor VII. Activated factor VII in turn activates factor X, followed by an activation of factor V and factor II (prothrombin). Factor IIa (thrombin) converts fibrinogen into fibrin at the end of the cascade.
The other route, the so-called intrinsic blood coagulation, occurs via an activation of factor XII by contact with and subsequent activation of factor XI, factor IX and factor X in the presence of calcium and factor VIII, followed by an activation of factor II to factor IIa which triggers the coagulation by cleaving fibrinogen to fibrin. Thus, factor IIa plays a central role in both routes of the blood coagulation cascade. Hitherto, there has been an intensive search for anticoagulants which may particularly be utilized in the treatment of septic shock, thromboses, embolisms, arteriosclerosis and cardiac infarctions, furthermore in case of blood transfusions or following surgery. One method of suppressing the coagulation of blood is the direct administration of substances which inhibit thrombin.
Hitherto, heparin or coumarin have been utilized as anticoagulants. They are, however, relatively systemic and increase the risk of inner hemorrhages. Hirudin, on the other hand, is extremely specific in its binding to thrombin and offers further advantages as compared to the other anticoagulants. It does not require endogenous cofactors, is pharmacodynamically inert, exhibits no effect on blood cells, plasma proteins (with the exception of thrombin) or enzymes, and is immunogenic on account of its small molecular size.
Furthermore, hirudin is not stored in organs and is excreted unchanged in urine.
Hirudin is a single-chain polypeptide of 65 amino acids which is naturally formed by the medicinal leech (Hirudo medicinalis) in its secretory glands. Hirudin acts as extremely strongly binding and highly specific inhibitor for the protease thrombin and prevents blood coagulation. The mechanism of the effect of hirudin as thrombin inhibitor has been cleared up: The C-terminal part of hirudin binds to the anion binding sites of the thrombin and thus occupies the binding site of the fibrinogen chain on thrombin. In addition, the N-terminal part of hirudin blocks the active site of thrombin (Szyperski et al.
1992, J. Mol. Biol. 228: 1206-1211; Fenton et al. 1991, Blood Coagul. Fibrinol.2: 69-75; Rydel et al. 1990, Science 249: 277-280; Karshikov et al. 1992, Prot. Science 1: 727-735; Markwardt 1991, Thromb. Haemost. 66: 141-152). For this reason, there has already been an interest for quite some time in using hirudin as a specific anticoagulant.
Recently it has been possible to prepare large amounts of hirudin by a recombinant route, and to use them for' pharmacological investigations (Rigel et al. 1993, Circl. Res.
72: 1091-1102; Loison et al. 1988, Biotechnol. 6: 72-77;
Zawilska et al. 1993, Thromb. Res. 69: 315-320; Klocking et al.
1990, Blut 60: 129; Fareed and Walenga 1989, FASEB J. 3: 328;
Markwardt et al. 1988, Pharmazie 43: 202-207). There result several clinical applications for hirudin: in hemodialysis, as an anticoagulant during the pulmonary transluminal coronary angioplasty (PTCA), for the prophylaxis of post-operative thrombosis, for the prevention of rethrombosis, for microvascular surgery, as anticoagulant in hemodialysis and in case of extracorporeal circulation, as an admixture to thrombolytic agents, such as, e.g., plasminogen activators and streptokinase, as anticoagulant during surgery and for the clinical suppression of coagulation.
When administering anticoagulants, exact dosing, however, is difficult. For instance, the inhibition of thrombin in the circulation of blood caused by hirudin can lead to undesired complications and hemorrhages requiring an immediate elimination of hirudin from circulation (Fareed et al. 1991, Sem. Thromb.
Hemost. 17: 137-144; Bruggener et al. 1989, Pharmazie 44: 648-649; Fareed and Walenga 1989, FASEB J. 3: 328). Yet the determination of the hirudin level (differentiation of free and bound hirudin) in the blood and monitoring the course of the hirudin excretion are possible only indirectly via the determination of the thrombin activity. At present, it is only possible to reduce the hirudin level in blood by natural excretion and, optionally, by means of dialysis. The administration of prothrombin has also been suggested (Walenga et al. Sem. Thromb. Hemost. 15:316:1989), yet the conversion of prothrombin into thrombin is time-dependent in circulation. On the other hand, an excess of thrombin favours the coagulation tendency. Not least of all, hirudin does form a very strong complex with thrombin which is difficult to dissociate even in vitro so that dosing of the hirudin level via a displacement mechanism realistically has not been practicable so far.
Thus there has been an intensive search in the prior art for a suitable antagonist to hirudin which can be used purposefully and thus does not exhibit side effects as regards blood coagulation. Although this has been a known problem of hirudin research (Markwardt F., Haemostasis 21:11; 1991), to date there have not been any practicable solutions which could be used in mediclne .
It has been suggested (Bruggener et al., Pharmazie 44:648;
1989) to carry out a chemical change of the thrombin. For this, diisopropyl fluorophosphate that has been purified from plasma was coupled to thrombin. DIP accumulates at the active site of thrombin, thereby changing the three-dimensional structure of the catalytic region. The DIP-thrombin formed is enzymatically inactive, yet binds hirudin. However, diisopropyl fluoro-phosphate is extremely toxic and dangerous. Since the binding of DIP to thrombin is not very stable, DIP can easily dissociate therefrom. A DIP-thrombin complex disintegrating in vivo thus is completely unsuitable for a clinical application.
In WO 93/15757 prothrombin intermediates have been suggested as antidotes to hirudin. However, these products comprise the usual risks generally inherent in preparations obtained from plasma, e.g. contamination by human pathogenic viruses.
Beside the use of heparin, coumarin and hirudin for preventing blood coagulation, also synthetic thrombin inhibitors, such as NAPAP (Na-(2-naphthyl-sulfuryl-glycyl)-D,L-amidinophenyl-alanin peptide) or PPACK (D-Phe-Pro-Arg-CHCl) are known. Furthermore, it has i.a.~been contemplated to use modified proteins, such as, e.g., inactivated coagulation factors, directly as anticoagulants. There, one particular problem is that in vivo the modified protein possibly could be eliminated from blood more rapidly than the wild type protein.
The coagulation process, comprising the cooperation of the intrinsic and extrinsic blood coagulation cascade and cell surface receptors, is very complex. Thus, apart from its greatly reduced or completely inhibited coagulation activity, an inactivated coagulation factor usable in vivo for therapy or prophylaxis should not differ from the natural protein in any further essential property, such as, e.g., receptor binding capacity. An in vivo half-life of the inactive protein corresponding to that of the active coagulation factor or even longer than that would be desirable. Since particularly thrombin has a very short half-life in vivo, an inactive coagulation factor having an extended half-life would increasingly displace the active protein, e.g. thrombin, from its receptor in case of a competitive inhibition. This would have the advantage that merely a relatively low dose would have to be administered for an efficient anticoagulant action of the inactive protein.
The present invention thus has as its object to provide a medically usable antagonist of hirudin which is substantially free from an enzymatic activity that promotes blood coagulation.
A further object of the present invention consists in providing an inactive coagulation factor which, in terms of its essential properties, such as, e.g., receptor binding capacity, does not differ from the natural protein and whose in vivo half-life optionally is increased.
According to the invention, this object is achieved by new prothrombin mutants or derivatives thereof which have one or more changes in their protein sequence as compared to the natural protein, are either inactive or have an activity of approximately 10~ at the most, preferably approximately 0.25~ at the most, of the natural protein and in which the change of the protein sequence does not affect their binding capacity to thrombin-specific ligands and receptors, such as natural and synthetic anticoagulants. Functionally, the inventive prothrombin mutants or their derivatives do not differ from their naturally occurring protein except for a greatly or completely reduced coagulation activity and optionally a changed in vivo half-life.
Within the scope of the present invention, by mutated prothrombin mutants or derivatives thereof, all the proteins derivable from the protein sequence of prothrombin are to be understood which exhibit the essential binding determinants of thrombin that are necessary for binding to the thrombin-specific natural and synthetic anticoagulants. Thus, the structure of the prothrombin mutant possibly should not be changed too much by the mutations as compared to wild type protein or its proteolytic derivatives, respectively, so that an optimum binding to the ligands, in particular to the natural ligands, is ensured.
Thus, an essential prerequisite for the mutants and derivatives according to the invention is that the change of the protein sequence does not affect their binding capacity to thrombin-specific ligands and receptors, such as natural and synthetic anticoagulants.
It has to be assumed that the mutants or derivatives, respectively, according to the invention must have a binding capacity of at least 80~ of the binding capacity of natural thrombin, so that the binding capacity can be considered as not affected. Also mutants and derivatives, respectively, which have a higher binding capacity than natural thrombin are, of course, also within the scope of the present invention.
The amount of binding capacity can be analyzed by any suitable method, e.g. by anticoagulants-competitive analysis between mutant or derivative, respectively, and natural thrombin (Gan et al., 1993), by assays relating to the binding affinity relative to artificial inhibitors (e.g. with DAPA (=dansyl arginine-N-(3-ethyl-1,5-pentandiyl) amide); Pei et al., J. Biol.
Chem. 266: 9598, 1991), or by means of tests of the binding affinity on an immobilized natural and synthetic anticoagulant or inhibitor, respectively.
In case of the latter, the natural or synthetic anticoagulant or the inhibitor, respectively, is immobilized on a solid matrix, a sample containing a certain amount of the derivative to be assayed is contacted with the natural and the synthetic anticoagulant or the inhibitor, respectively, the amount of bound mutant or derivative, respectively, is determined, and the results are correlated by means of a parallel determination with natural thrombin.
The mutants or derivatives, respectively, according to the invention preferably should be entirely inactive, i.e. they should not have any thrombin or thrombin-analogous activity.
However, derivatives having a slight activity can also be used successfully according to the invention, since an activity of approximately 10~ at the most, in particular 0.25~ at the most, of natural thrombin generally does not lead to the undesired side effects, such as, e.g., coagulation tendency, when the derivatives according to the invention are administered.
The mutants or derivatives, respectively, according to the invention are further characterized in that they can form a complex with hirudin and thus are able to neutralize hirudin.
Furthermore, they can dissociate a complex consisting of plasmatic or recombinant wt-thrombin with hirudin, and complex the thus liberated hirudin. From this follows furthermore that the liberated plasmatic or recombinant wild type (wt) thrombin is active again and can fulfill its task in blood coagulation.
Also according to the invention this is a necessary parameter for the therapeutic use of the thrombin derivatives.
Preferred embodiments of the mutants or derivatives, respectively, according to the invention have an in vivo half-life of more than one hour.
Other preferred embodiments have an in vivo half-life of 10 minutes at the most.
The change of the amino acid sequence may consist of an exchange of one or more amino acids, it may, however, also consist of a deletion, preferably a deletion corresponding to the processing procedure during the activation of prothrombin, or of an insertion, if by these changes the parameter essential to the invention, an activity of approximately 10~ at the most, in particular of 0.25~ at the most, of natural thrombin, and an almost unchanged binding to thrombin ligands and -receptors, are met. The term "derivative" is meant to include both the proteins changed merely by mutation and the processed mutant proteins.
For the exchange of amino acids, those are best suited as amino acids to be introduced which have as little influence as possible on the spacial structure of the protein. These are either very small amino acids, such as alanin, or amino acids which are very similar to the original amino acid and differ therefrom only by one functional group, e.g. asparagine and aspartic acid.
The parameters according to the invention make the mutants or derivatives, respectively, mentioned to ideal thrombin inhibitor antagonists, since they do not have the disadvantages mentioned in the prior art, i.e. an undesired coagulation activity, toxicity or a lack of efficiency or specificity, respectively.
Since the inventive mutants or derivatives, respectively, are inactive or have an activity of approximately 10~ at the most, in particular approximately 0.25~ at the most, of natural thrombin (whereby the in vivo thrombin activity of the mutants or derivatives, respectively, is even considerably lower than these approximately 0.25~), they cannot lead to undesired coagulation effects even if they are administered in an overdose.
For the mutants or derivatives, respectively, according to the invention, a toxic effect is not to be expected, since they hardly differ from the natural proteins and thus can be metabolized normally.
The mutants or derivatives, respectively, according to the invention are highly efficient and highly specific as antagonists, since their binding determinants to natural and synthetic inhibitors are substantially unchanged and correspond to those of natural thrombin.
Preferred changes of the protein sequence concern amino acids from the active site of the prothrombin, meizothrombin or thrombin molecule, in particular the amino acids His-363 and Asp-419, based on the amino acid numbering in human prothrombin according to Fig. 1. (The numbering of the amino acids in general is according to Fig. 1, in which the cDNA sequence and the amino acid sequence of prothrombin are shown. The cleavage sites of factor Xa are indicated in the cDNA sequence so that the cDNA and amino acid sequence of thrombin can be derived.
Numbering starts with the 1st amino acid of the mature prothrombin after cleavage of the leader sequence and the . CA 02224634 1997-12-12 .

propeptide. The cDNA sequence of prothrombin is illustrated in SEQ.ID.NO.8, the amino acid sequence in SEQ.ID.NO.9.).
Particularly the amino acid Aspartic acid-419 (Asp-419) has no close contact to bound hirudin, and therefore the exchange of this amino acid is particularly preferred within the scope of the present invention.
In addition, the changes relating to the cystein residues Cys-293 and Cys-439, based on the amino acid numbering in prothrombin according to Fig. 1, are also preferred. These mutations enable the formation of a single-chain thrombin derivative (since the sulphur bridge bond between the B-chain and the A-chain is prevented), which finally does not have any enzymatic activity despite its binding capacity to hirudin (since the A-chain is missing). In this case, the amino acids serine and alanine offer themselves as exchange partners.
Since all these selected derivatives have mutations which directly concern the catalytic center or concern disulfide bonds important for the function of thrombin, respectively, they are inactive. As can be seen by way of structural data (Rydel et al., 1990), these amino acids neither concern regions that concern the binding of natural and synthetic inhibitors, in particular hirudin.
Thus, the invention preferably relates to prothrombin mutants or -derivatives in which at least one amino acid selected from His-363 or Asp-419 and optionally Cys-293 or Cys-439, has been changed, in particular Asp-419-mutants.
A particularly preferred embodiment of the mutants or derivatives, respectively, according to the invention relates to mutants or derivatives, respectively, in which the amino acid Asp-419 has been exchanged for Asn.
It has been shown that this variant is inactive, even towards the synthetic substrate AcOH-H-D-CHG-Ala-Arg-pNA it has merely a residual activity of approximately 0.25~, so that no coagulation-active side effects whatsoever are to be expected.
Furthermore, the binding capacity of this derivative, e.g.
relative to hirudin, cannot be differentiated from that of natural thrombin, since the structural changes brought about by the exchange of Asp for Asn is very slight and moreover is localized in a region of the protein which does not concern the . CA 02224634 1997-12-12 g binding to the natural and synthetic inhibitors, in particular hirudin.
Mutant prothrombines have been described in the prior art, yet derivatives exhibiting the properties claimed have not yet been disclosed. Yet it is just these properties that make the use of the prothrombin, meizothrombin and thrombin derivatives according to the invention so very advantageous.
A series of genetic defects have, e.g., been described which relate to prothrombins and thrombins resulting therefrom with point mutations, the various mutants having a drastically reduced blood coagulation activity (Henriksen R.A., Methods in Enzymology, Vol. 222:312 (1993)). Yet all these mutations concern changes in which a certain - though reduced - thrombin activity is still found (particularly relative to synthetic substrates). Yet it is probably this residual activity which allows for the survival of persons suffering from these defects, and from this it follows that a mutation that leads to an entirely inactive thrombin probably is not capable of surviving.
Furthermore, in vitro point mutations have been carried out in the prothrombin- and thrombin sequence so as to carry out structural and functional analyses:
For instance, Serine-528 at the active site of bovine prothrombin (equivalent to Serine-525 in the corresponding human prothrombin) has been mutated to an alanine. With such a mutant prothrombin, experiments relating to the fundamentals of science have been carried out to study the influence of this mutation on the expression, ~-carboxylation and activation of prothrombin.
The structural analysis of the thrombin-hirudin complex has shown that also amino acids from the active site of thrombin contribute slightly to the formation of the complex. Thus, in particular Ser-525 in human prothrombin may form hydrogen bridges to the N-terminal amino acid of hirudin and may be within the radius of 3.2 A from the N-terminus of hirudin. Thus, Ser-525 apparently contributes to the bonding of hirudin (Rydel at al., Science 249:277, 1990).
Furthermore, it has been found that the bovine Ser-528 variant merely has a 74~ binding capacity relative to DAPA, as compared to natural thrombin. This was proof of the assumption that this serine residue is located immediately in the DAPA or hirudin binding determinant, respectively. Therefore, mutations which merely concern the Ser-528 site in bovine prothrombin or the Ser-525 site in human prothrombin, respectively, do not meet the requirement of the sufficient binding capacity to the inhibitor.
Furthermore, thrombin fragments with longer deletions have been prepared (Gan et al., Arch. Biochem. Biophys. 1993:301, 228). A degradation product of thrombin, ~-thrombin, is obtained which comprises the amino acids 469 to 579 of the ~-thrombin sequence. For functional studies, the amino acids Arginine-517 (to glutamine), and Serine-525 (to alanine), respectively, were mutated, and there a slighter activity was found in the individual mutants than in wild type thrombin. The hirudin binding capacity was only partly maintained in some ~-thrombins.
The Ser-525-Ala mutant did exhibit the least enzymatic activity and the best results in terms of hirudin binding, yet also in these studies the binding capacity was clearly below that of natural thrombin. It has been shown that in competitive binding studies the thrombin fragments compete to different degrees with a thrombin-hirudin binding, and there are no absolute data regarding the binding capacity of the fragments to hirudin, yet the results clearly show that the binding capacity to hirudin has been markedly reduced by the mutation.
Thus, these ~-thrombins are not suitable for the object underlying the invention: as compared to wild type thrombins, they are greatly changed, and an optimum bonding to the natural ligands cannot be guaranteed.
Thus, it has not been possible to meet the required parameters with the prothrombin- or thrombin derivatives, respectively, described in the prior art.
Neither can any data be found in these citations as to a possible therapeutic or diagnostic utilization of these prothrombin mutants (derivatives) or ~-thrombin fragments.
Thus, according to another aspect, the present invention relates to the use of prothrombin mutants or derivatives thereof as medicaments, in particular for producing a medical preparation for preventing the side effects in an anticoagulation treatment, or as diagnostic agents. This use according to the invention of the mutants or derivatives, respectively, is particularly preferred in the anticoagulation treatment with hirudin, heparin, antithrombin III and/or the derivatives thereof, as well as synthetic inhibitors.
The medical treatment according to the invention thus comprises administering an effective dose of the prothrombin mutant or derivatives thereof to a patient, preferably intravenously. The effective dose will depend on each individual single case and preferably should be optimized by using the results obtained from a thrombin and/or hirudin determination.
Naturally, with the use according to the invention, the prothrombin mutants or derivatives, respectively, having the properties according to the invention as regards a deficient thrombin activity and a sufficient binding capacity are preferably used, yet under certain conditions also known derivatives can be utilized, in particular those which are largely inactive, such as, e.g., an analogue to the above-described bovine Ser-528 mutant (or its thrombin derivative, respectively), in which case, however, the drawback of the inferior binding capacity must be put up with.
It has generally been known that the in vivo half-life of the proteins in blood circulation is influenced by glycosylation. Proteins from mammalian cells thus may be present in glycosylated form via protein-surface-localized amino acid side-chains of asparagine (N-glycosylation) and serine/threonine (O-glycosylation. By the glycosylation of circulating proteins, a delay of their elimination from circulation, i.e. an extension of their half-life, is attained. Recombinant proteins prepared by manipulating mammalian cells by their nature are provided with the glycosylations common and natural for mammals and thus correspond to the surface structure of the corresponding human proteins.
By mutation of amino acids located at the surface of a protein, such as, e.g. asparagine (Asn) and serine (Ser), respectively, or threonine (Thr), into a different amino acid, or by deletion of one of these amino acids, it is, e.g., possible to prevent native glycosylation. It is known that slightly or non-glycosylated proteins are much more rapidly eliminated from circulation, i.e. that their half-life is shortened.

To the contrary, by mutation and amino acid exchange of individual amino acids located at the protein surface, the number of glycosylation sites of a protein molecule may be increased, e.g. in asparagine, and thus also the in vivo half-like can be increased. Depending on the number of mutant, deleted or additionally inserted asparagine residues in the protein, the half-life thus optionally can be varied.
For the use according to the invention of the prothrombin mutants or derivatives thereof as antagonists relative to thrombin inhibitors, those mutants are particularly suitable, in which the half-life of the protein has been shortened by mutation. Preferably, thus, those mutants are used as antagonists which have a half-life of 10 minutes at the most.
The medical use according to the invention of the mutated prothrombin mutants or derivatives, respectively, also comprises their use as anticoagulants by competitive inhibition of thrombin, or as antagonists of their natural functions, respectively. This enables medical control of the blood coagulation by means of a product which is nearly identical to nature.
On account of the parameters according to the invention and of the unchanged binding capacity to specific receptors and ligands, prothrombin mutants or their derivatives are particularly useful as anticoagulants in vivo.
For the use according to the invention of the prothrombin mutants or derivatives thereof as anticoagulants, such mutants are particularly useful in which the half-life of the protein is increased by a purposeful amino acid exchange. Thus, preferably those inactive mutants are used as anticoagulants which have a half-life of more than 1 hour.
When using the prothrombin mutants of the invention as anticoagulants, they are processed after their application, corresponding to natural protein, in vivo to inactive thrombin which then is able to displace active thrombin occurring in blood from its receptors. The prothrombin mutant may optionally also be activated in vitro to the corresponding thrombin or meizothrombin mutant, and the activated form may directly be used for administration to the patient. Depending on the dosage of the prothrombin mutant or their derivatives according to the invention in a medicament, the blood coagulation can be slowed or completely stopped in vivo. The use of prothrombin mutants or derivatives thereof which are characterized by an increased in vivo half-life have the particular advantage that they circulate in blood substantially longer than their natural protein counterparts and thus can effectively influence blood coagulation. Moreover, for an effective anticoagulant action, the amount of therapeutically used protein may optionally also be correspondingly reduced.
For the in vivo application of the inventive prothrombin mutants or their derivatives as anticoagulants, a toxic side effect is not to be expected, since they are normally metabolized in vivo in accordance with their natural proteins.
The mutant prothrombin derivatives according to the invention may preferably be prepared by using recombinant DNA
technology. Thus, the invention also relates to a method of preparing the inventive prothrombin mutants or their derivatives, respectively, in which the genetic information of prothrombin is mutated, preferably point-mutated, and expressed in a eukaryotic expression system, whereupon the expressed derivative is recovered.
There, preferably, human sequences are used.
In contrast to bacterial systems, the expression in eukaryotic systems has the advantage that also post-translational modifications, such as glycosylation and carboxylation, are carried out, and thus the expressed protein is better suited for an application on man.
For the recovery of the peptides in Gan et al., the mutated sequence portions of thrombin are expressed in E. coli, and the recombinant peptides are artificially provided with sulphur bridges in vitro. Accordingly, the yield of expressed thrombin-like structures suitable for tests was very low. The loss of the thrombin activity may be due to the absence of large parts of the thrombin sequence just as well as to the introduced mutations.
The expression in E. coli, as described in Gan et al., is not suitable for proteins having the properties according to the invention, since this expression system does not effect glycosylation, and also the folding of the expressed proteins does not correspond to the physiological structure. According to the invention, however, as few changes as possible should be made in the derivatives, as compared to wild type thrombin. For the functional studies in Gan et al. it is, however, without importance that the expressed ~-thrombins do not comprise carbohydrates, on the one hand (the only glycosylation site in physiologic thrombin (Asparagine-53) was missing), and that the folding of the peptide in vitro has been carried out in a complicated way. This method leads only to extremely low yields.
In a method according to the present invention, the cDNA-sequence of human prothrombin or the cDNA-sequence of human thrombin preferably is point-mutated, whereby an exchange of at least one amino acid in the amino acid sequence is brought about. In the case of prothrombin, the site of mutation according to the invention is to be found in the region of the prothrombin sequence which, after activation of the prothrombin, lies in the thrombin sequence.
Preferably, the mutant prothrombin derivatives are expressed under the control of the SV40 promoter in CHO-DUXS B11 cells (Urlaub ~ Chasin, Proc. Natl. Acad. Sci. USA 77:4216, 1980).
Yet, the expression may be effected with any common expression system, such as yeast, permanent cell lines or viral expression systems, and with any desired cell line which ensures that the protein is correctly processed and secreted in its functional form. Correct processing of the derivatives does not only encompass the complete glycosylation, but also the complete ~-carboxylation. Among the common eukaryotic expression systems are yeast, permanent cell lines (which have either been established by stable integration of the foreign-DNA in the chromosomes of the host cells, e.g. Vero, MRC5, CHO, BHK, 293, Sk-Hepl, in particular liver and kidney cells, or by using a vector which is permanently inherited in episomal state, e.g.
vectors which are derived from papilloma viruses and grow, e.g., in C-127 cells), or viral expression systems, such as vaccinia virus, baculovirus or retroviral systems. As the cell lines, generally Vero, MRC5, CHO, BHK, 293, Sk-Hep-1, in particular liver and kidney cells, may be used.
Following the recovery of the expressed derivatives, still further processing steps may be carried out. One possibility of CA 02224634 l997-l2-l2 further processing prothrombin mutants or derivatives thereof, respectively, is a process step in which the prothrombin derivative is cleaved into meizothrombin analogues by means of a snake venom protease (e.g. Venom Protease). These meizothrombin analogues then also can be used as antagonists to the natural functions of thrombin, yet they do not exhibit an enzymatic thrombin activity. In this connection, all the methods known from the literature can be used.
Furthermore, a prothrombin derivative obtained may be cleaved into the thrombin derivative by means of trypsin, preferably immobilized trypsin. Yet, naturally any other common method of cleaving prothrombin to thrombin may be used, even those which use other suitable proteases, e.g. the snake venom from E. carinatue (Ecarin) or from O. scwtellatus.
To process the preparations, the derivatives according to the invention are either prepared with physiologic saline solution and optionally lyophilized, or they are lyophilized in distilled water and reconstituted with physiological saline solution before being administered. Alternatively, the preparations may also be kept available for use in other common solutions and/or with a pharmaceutical carrier or auxiliary agent.
According to the invention, the preparations are present in a form suitable for parenteral administration, i.e. for subcutaneous, intramuscular or intravenous administration.
A further advantage of the preparations according to the invention which must not be neglected consists in that on account of their production they are free from contaminations by viruses. Before being released for medical applications, the preparations may additionally be assayed for a possible contamination by residual nucleic acids of the expression cell line by means of a highly sensitive PCR method (e.g. disclosed in Austrian Patent Application A 1830/94), and if necessary, they may be purified once more.
Finally, the derivatives according to the invention must be tested for their capability of binding their natural ligands.
Within the scope of the present invention, a test system has been worked out for this, in which the binding capacity of the (Pro-)thrombin derivatives to hirudin or hirudin derivatives is qualitatively and quantitatively analysed in a simple and reproducible manner. This test system consists in a solid matrix to which natural or recombinant hirudin, derivatives or peptides thereof are bound. Finally, the derivative according to the invention is bound to this immobilized hirudin and may be detected in a subsequent detection reaction.
Therefore, the invention also relates to a solid matrix to which natural or recombinant hirudin, derivatives or peptides thereof are bound, and their use in the determination of thrombin or thrombin derivatives. The determination may comprise both the quantitation and the determination of the binding capacity of the thrombin or thrombin derivative.
As solid matrix according to the invention any solid phase is to be understood, at which the natural and synthetic inhibitor can effectively be immobilized, e.g. natural polymers, such as cellulose, starch, dextrane, alginates, agarose, collagen, in particular the sepharose and cellulose materials, repsectively, widely used in immobilization technology, synthetic polymers, such as polyacryl amide, polyvinyl alcohol, methylacrylate, nylon or oxiranes which can easily be shaped to user-friendly devices, such as, e.g., microtiter plates, and finally inorganic materials, such as porous glasses, siliga gel, etc. (cf. also Rompp-Lexikon der Biotechnologie, pp. 385).
With the device according to the invention, a simple and precise determination of the thrombin or thrombin derivative concentration, respectively, can be effected, wherein not only the active thrombin itself can be determined, but also enzymatically inactive or only slightly active prothrombin or thrombin and derivatives therof. Furthermore, on account of its user-friendly design, the device according to the invention may also be indirectly used for the determination of the concentration of any thrombin-binding substances, such as thrombin inhibitors, yet particularly hirudin. Moreover, also a determination of the binding strength of thrombin or thrombin derivatives to the respective tested natural and synthetic inhibitors is feasible with the device according to the invention.
As thrombin or thrombin derivatives, all the proteins derivable from the protein sequence of prothrombin are to be understood within the scope of the present invention, in particular the mutant thrombin, meizothrombin or prothrombin derivatives described above. In this connection, the derivative can also be altered at the binding determinants, as long as this change does not exclude a bonding to the natural and synthetic inhibitors. The thrombin derivatives may differ from natural thrombin by one or more point deletion- or insertion mutations.
Prothrombin derivatives, meizothrombin as well as the derivatives thereof may also be determined by means of the device according to the invention and are also to be viewed as thrombin derivatives within the scope of the present invention -insofar as their determination is concerned.
For the quantitation proper of thrombin, thrombin derivatives and/or hirudin or hirudin derivatives, according to the invention a test kit is provided which contains the device according to the invention as well as one or more containers with reagents for a specific detection reaction, preferably a thrombin-derivative-specific detection reaction. By specific detection reaction, any suitable detection reaction is to be understood, in particular those reactions which work with dyes (peroxidase, alkaline phosphatase, luminiscence reactions, biotin, avidin or biotin-streptavidin (as enhancer systems)) or radioactive determination methods.
For a determination of the concentration, preferably, the colour reaction which is simpler to handle is preferred to the radioactive determination. In particular, the peroxidase-labelled sheep-anti-thrombin-antibodies are used for the invention, and the substrate solutions common for the peroxidase reaction are used for the colour reaction.
The test kit according to the invention further includes a container with a physiologic buffer solution containing a carrier protein, whereby the reproducibility of the quantitation is substantially improved.
The specific detection reaction within the scope of the test kit of the invention preferably is a labelled thrombin-binding substance, since in the clinic, the determination of thrombin frequently is of primary importance as compared to the other determinable components. In the prior art a large number of labelled thrombin-binding substances is known. According to the invention, a dye-labelled polyclonal or monoclonal antibody to thrombin preferably is used. Detection by means of chromogenic substances is frequently preferred to radioactive determination methods, since the dye reactions do not entrain a radioactive contamination and since the rigid safety measures required when working with radioactive material very often render the radioactive determination method very impractical.
The detection method may take place according to the method steps common in protein chemistry. To determine the concentration of thrombin or thrombin derivatives, a thrombin solution is incubated for 15 minutes to 16 hours, preferably between 45 minutes and 4 hours, with the hirudin-coupled solid matrix. Usually, the reaction takes place in a physiologic buffer, preferably in a Tris-HCl buffer. It is particularly advantageous if a carrier protein, such as albumin, e.g., is admisted to the physiologic salt buffer.
A preferred embodiment of the test kit according to the invention further comprises a thrombin-containing reference solution which allows for the establishment of a reliable calibration straight line in the test system.
According to a further aspect, the invention relates to a method of quantitating thrombin or thrombin derivatives, which is characterized by the following steps:
- incubating a solution which contains the amount of thrombin or thrombin derivatives to be quantitated with hirudin or a hirudin derivative which is immobilized on a solid matrix, the thrombin or derivative becoming bound to the immobilized hirudin or hirudin derivative, - optionally removing non-bound thrombin or thrombin derivative, - carrying out a specific detection reaction, the amount of bound thrombin or thrombin derivative being determined.
Carrying out the specific detection reaction may be effected either within the scope of the test kit according to the invention with the reagents for a specific detection reaction, or directly by a measuring device on the solid matrix itself, such as a sensor chip with a measuring installation connected therewith.
The method according to the invention may be carried out in a simple manner, it being particularly suited for the rapid and uncomplicated application in the clinical field.
A preferred embodiment of the method according to the invention relates to a method in which the specific detection reaction is a colour reaction, the concentration of thrombin or thrombin derivative being determined by correlation with the intensity of the colour reaction.
According to a further aspect, the method according to the invention also is suitable for quantitating hirudin or hirudin derivatives, such a method being characterized by the following steps:
- incubating a solution comprising an amount of hirudin or hirudin derivative to be quantitated with a solution comprising a known amount of free thrombin or thrombin derivative, - determining the free thrombin or thrombin derivative concentration remaining after incubation with the hirudin or hirudin derivative by means of the above-described method of the invention, and - determining the amount of hirudin or hirudin derivative by calculating back on the basis of the differences between the amount of thrombin or thrombin derivative originally known and the amount determined.
According to a further aspect, the present invention relates to the use of a device according to the invention or of the test kit of the invention, respectively, for quantitating thrombin, thrombin derivatives and/or hirudin or hirudin derivatives as well as for determining the binding strength of thrombin or thrombin derivatives to hirudin or hirudin derivatives.
For, surprisingly, it has been shown that with this test kit it is possible for the first time also to determine the binding strength of thrombin or thrombin derivatives to hirudin or other thrombin-hampering substances. The binding strength of thrombin to hirudin primarily is of interest in case of thrombin derivatives whose binding properties to hirudin are unknown.
Furthermore, the test kit may be used for a function analysis of hirudin antagonists. When testing hirudin peptides or hirudin derivatives as effective anticoagulants, this method can also be applied.

The test kit according to the invention thus is suitable to answer all the questions arising in connection with thrombin, hirudin and the coagulation of blood in terms of concentration, binding strength and functionality. There, it must be particularly emphasized that due to the specificity of the binding of hirudin to thrombin, it is possible to obtain an extremely exact result. Impurities by other blood factors or proteins cannot falsify the result. Neither does the presence of prothrombin interfere with the analyses, since prothrombin does not bind to hirudin.
Although it has been known to couple hirudin to microtiter plates so as to test anti-hirudin-antibodies with these ELISA
plates, a quantitation or determination of the binding capacity by aid of these plates has not yet been described. (Mille B. et al., Clin.Chem. 40:734, 1994).
When preparing a hirudin-coupled solid matrix, hirudin is coupled to the matrix in a buffer system.
Any buffer that is free from amino groups is suitable as buffer system, such as phosphate buffer, citrated buffer or preferably carbonate buffer. The pH of the buffer system should be in an amount of between 6 and 10, preferably at pH 9.3 to 9.7.
According to the invention, in the coupling reaction of hirudin to the solid carrier, it is incubated between one and 48 hours, preferably between one and 16 hours. The incubation time substantially depends on the incubation temperature, and in a coupling reaction, the incubation preferably takes place for 16 hours in the cold (4~C), for two to three hours at room temperature, and for one hour at 37~C.
After the coupling reaction, according to the invention the excess non-bound hirudin is removed by means of a washing buffer comprised of a physiologic saline solution, preferably a Tris-HC1 buffer. To this washing buffer a detergent, preferably Tween 20, may be added, the detergent concentration lying between 0.01 and 1~, preferably at 0.1 ~.
With the test kit according to the invention, concentrations of thrombin or thrombin derivatives in the range of from 0.1 pg/ml to 100 mg/ml, preferably in the range of from 0.1 ng/ml to 200 ng/ml thrombin, can be determined.

Not least of all, the inventive test kit is suitable for differentiating between thrombins with recombinant designed, purposeful mutations, deletions or insertions, it being possible to test whether or not the binding ability to hirudin has been maintained irrespective of the enzymatic activity.
This test according to the invention of the inventive test kit may especially be used if the thrombin level in blood is to be determined in case of a particular medical problem, so as to prevent thromboses by an exactly dosed administration of hirudin.
Furthermore, this test has the particular advantage that also thrombin can be determined which is not funcionally active and which thus is not detectable in tests that register the enzymatic activity of thrombin. This is, e.g., so in case of genetic defects, where there are physiologically inactive forms of thrombin.
The invention will now be explained in more detail and with reference to the following Examples and associated drawing figures to which, however, it shall not be restricted.
Fig. 1 shows the encoding part of the cDNA sequence of recombinant human prothrombin and the amino acid sequence derivable therefrom, the physological cleavage sites for processing the protein and the cleavage sites of factor Xa, respectively, for activating the prothrombin to thrombin being entered;
Fig. 2 shows the sequence listing;
Fig. 3 shows a summary of the point mutation of a preferred prothrombin derivative as compared to wt-prothrombin, the underlined amino acid/nucleotides having been exchanged;
Fig. 4a shows the flow diagram of the cloning of prothrombin-Asn419;
Fig. 4B shows a Western blot to compare plasmatic prothrombin, recombinant wt-prothrombin and prothrombin-Asn419;
Fig. 5 represents the denaturing electrophoresis of individual purification stages of recombinant prothrombin derivatives (A: cell culture supernatant; B: eluate 3; C: eluate 4;D: molecular weight marker);
Fig. 6 shows the denaturing electrophoresis of individual stages of the formation of Thrombin-Asn99 from Prothrombin-Asn419 (A: Prothrombin-Asn419; B: eluate 3; C: human thrombin;
D: molecular weight marker);
Fig. 7 shows the binding of Thrombin-Asn99 (A), recombinant wt-thrombin (B) and human plasmatic thrombin (C) to immobilized hirudin;
Fig. 8 indicates the dependence of the thrombin fluorescence on the hirudin concentration (the fluorescence at 341 nm (excitation 280 nm) of 390 nM Thrombin-Asn99 (A), 326 nM
recombinant wt-thrombin (B) and 350 nM human plasmatic thrombin (C) were determined in dependence on the hirudin concentration, the fluorescence without hirudin being illustrated as 0~, the fluorescence at hirudin saturation as 100~);
Fig. 9 shows the neutralization of hirudin by Thrombin-Asn99;
Fig. 10 shows the reconstitution of the thrombin activity from the hirudin-thrombin complex by the addition of Thrombin-Asn99 with different concentrations of Thrombin-Asn99: (A) 0.2 ~g/ml, (B) 0.4 ~g/ml, (C) 1 ~g/ml;
Fig. 11 shows the neutralization of hirudin in plasma (the clotting time in the presence of hirudin (x---x) and without the addition of hirudin ( ) being illustrated in the test in dependence on the concentration of Thrombin-Asn99);
Fig. 12 represents the molecular structure of the catalytic center in the thrombin-hirudin complex (comparison of human thrombin and recombinant thrombin derivative), the structural changes caused by the mutation Asp~Asn being indicated by arrows, and Ser, His and Asp or Asn, respectively, representing the position of the amino acids of the catalytic center in the thrombin molecule and Ile representing the N-terminal amino acid of hirudin.
Examples:
Example 1 shows the procedure by which a point-mutated prothrombin can be obtained, by way of the example prothrombin-Asn419. Example 2 demonstrates the purification and functional analysis of the prothrombin derivative. Example 3 shows the recovery and functional analysis of the thrombin derivative.
Example 4 quantitates the binding acitivity of the thrombin derivative to hirudin; Example 5 checks the prothrombin derivative for its ability of acting as an antagonist of hirudin, Example 6 shows that hirudin can be neutralized by the thrombin derivative. In Example 7 it is demonstrated that the thrombin derivative is able to re-activate the thrombin from a thrombin-hirudin complex; Example 8 shows that the thrombin derivative is also effective in plasma, and Example 9 shows the recovery and functional analysis of a meizothrombin derivative.
Example 1: Construction of pSV-FIIwt and pSV-FII-Asn419 (Asp to Asn) Plasmid pSV~ (Nucl. Acids Res. 17: 2365; 1989) was cleaved with NotI so as to remove the internal ~-galactosidase gene fragment. The remaining vector was religated and termed pSV.
To remove the largest part of the polylinker sequence located 3' to the polyadenylation site which might interfere later on, pSV was cleaved with HindIII and XbaI. After removal of the small polylinker fragment, the vector ends were filled up with klenow enzyme and religated. The resultant plasmid was termed pSV~.
Subsequently, a multiple cloning site (MCS) comprising suitable restriction cleavage sites was inserted in the XhoI
site located 5' of the 16/19S intron.
The MCS was chemically synthesized in the form of two complementary oligonucleotides:
5'-TCGACCATGG ACAAGCTTAT CGATCCCGGG AATTCGGTAC CGTCGACCTG
CAGGTGCACG GGCCCAGATC TGACTGACTG A-3' (Seq.ID.No.l) and 5'-TCGATCAGTC AGTCAGATCT GGGCCCGTGC ACCTGCAGGT CGACGGTACC
GAATTCCCGG GATCGATAAG CTTGTCCATG G-3' (Seq.ID.No.2) The two oligonucleotides were annealed and inserted in pSV~.
Since the MCS insert had XhoI-compatible, sticky ends, yet not complete XhoI-sites, the ligation reaction was cleaved with XhoI. Non-cleavable constructs represented the desired plasmid which was termed pSV-MCS III.
A DNA-fragment having the complete human wt-prothrombin-cDNA
was cut out of plasmid pTKemc-PT2 (WO 91/11519) by means of partial NcoI and complete SmaI restriction digests.
This fragment was inserted in vector pSV-MCS III, after the latter had also been completely opened via partial NcoI and complete SmaI digests.
The resultant plasmid was termed pSV-FIIwt and expresses wt-prothrombin, as detected by transient expression in COS cells and stable expression in CHO cells; the sequence of the functional elements of pSV-FIIwt is SV40-promoter/enhancer (of the early genes), SV40-5' UTR, wt-prothrombin-cDNA, SV40-16s/19s intron, SV40-polyadenylation site and pUC 19-sequences (with bacterial replication origin and ampicillin resistance gene).
To mutate the aspartic acid of the catalytic center of the thrombin to an asparagin and thus prepare an inactive mutant of the thrombin, pSV-FIIwt was mutated: The codon encoding for the said aspartic acid is located on an EcoRV-DraIII restriction fragment. Both restriction sites are uniquely present in pSV-FIIwt. The intended mutagenesis was carried out by means of polmerase chain reaction with the primer pair 2104/2066 (Seq.ID.Nos. 3 and 4), whereupon the wt-prothrombin-EcoRv-DraIII
fragment was substituted by the PCR Ecll36II-DraIII-fragment that contained the mutation.
The two oligonucleotides were chemically synthesized:
Primer 2104 (5'-TAACTGACGG TCCTTGAGCT CCATGTTGGA AAAGATCTAC ATC-3') (Seq.ID.No.3) as 5' primer; following the polymerase chain reaction, the Ec1136II half site is ligated to the EcoRV half site of the vector, by which some nucleotides of the wt-prothrombin were changed on DNA-level, yet the amino acid sequence is maintained as in wt-prothrombin.
Primer 2066 (5'-GCAGACACAC AGGGTGAATG TAGTCACTGA AGGCAACAGG
CTTCTTCAGC TTCATCAGGG CAATATTCCG GTCCAGGTTC TCCCGC-3') (Seq.ID.No.4) as 3' primer; by this primer, the aspartic acid is mutated to asparagine on DNA level, an SspI restriction site is introduced and an NciI site is lost.
The PC reaction was carried out under standard conditions at an annealing temperature of 55~C.
The resultant plasmid pSV-FIIAsn419 which contains the Asp~Asn mutation was identified by its restriction pattern with EcoRV, DraIII, SspI and NciI in comparison with pSV-FIIwt.
The flow diagram of the cloning route is shown in Fig.4A.
The expected nucleotide sequence of the Ecll36II-DraIII
insert in pSV-FIIAsn419 was confirmed by subsequent sequencing with the 5' and 3' primers 2197 (5'-CATAAGCCTG AAATCAACTC-3') (Seq.ID.No.5) and 2198 (5'-CTTCGGAGCG TGGAGTCATC-3') (Seq.ID.No.6), respectively.

Dihydrofolate reductase gene-deficient CHO-DUKS Bll routinely grow in complete medium (DMEM/Ham's F12 1:1 medium, supplemented with 2 mM glutamine, 0.075~ bicarbonate, 100 IU
penicillin and 100 mg of streptomycin/ml, 10~ fetal calf serum as well as 10 mg of deoxyadenosine, adenosine and thymidine per ml).
By means of a modified CaPO4 method (Graham and van der Eb, Virology 52: 456, 1973), the cells were cotransfected with 10 ~g of pSV-FIIwt and pSV-FIIAsn-419, respectively, and 1 ~g of pSV-dhfr (Fischer et al., FEBS Lett. 351:345, 1994): to the DNA in 250 ml of 1 mM Tris, pH 8,0, 0.1 mM EDTA, there were added 25 ml of 2.5 M CaCl2. Subsequently, 250 ml of 280 mM NaCl, 45 mM
Hepes, 2.8 mM Na2HPO4, pH 7.12, were added. After 10 minutes the DNA coprecipitate formed was added to the subconfluent cells.
Six hours later, the medium was sucked off, and the cells were overlaid with 15~ glycerol in PBS. One minute later, the glycerol was sucked off, the cells were washed with PBS, and the cells were provided with fresh complete medium.
48 hours later, the cells were trypsinized and partitioned in various concentrations in selection medium (DMEM/F12 1:1 medium without hypoxanthine glycine and thymidine; supplemented with 2 mM glutamine, 100IU penicillin and 100 mg of streptomycine/ml, and 10~ dialysed fetal calf serum with an exclusion volume of 10,000Kd). With a regular exchange of medium 2-3 times per week, cell clones were visible after approximately 10 days. After further week, the resultant cell clones were isolated and grown to confluence in separate cell culture dishes. In serum-free 24 hour cell culture supernatants with secreted, recombinant wt prothrombin or prothrombinAsn419, respectively, in selection medium (supplemented with 10 ~g of vitamin Kl/ml, yet without calf serum), subsequently the antigen amount and qualitative integrity (Western blot analysis), functionality (suitable activity tests~ and interaction of the prothrombin, activated to thrombin, with hirudin were examined.
The cell number was determined after trypsinization of the cells in the cell counter of Scharfe, Reutlingen, Germany.
For the Western blot analysis, 10 ~1 of cell culture supernatant were reduced and denatured, and partitioned in denaturing 4~ collecting-/8~ separating gels according to Lammli (Nature 227: pp. 680, 1970) by means of the BioRad Mini-Protean II Dual Slab Gel System (BioRad Laboratories, Richmond, CA, USA). After the gel run had been effected, the proteins were transferred in transfer buffer (25 mM Tris, 192 mM glycine) to nitrocellulose membranes by means of the BioRad Mini Trans-Blot-System (BioRad Laboratories, Richmond, CA, USA). The Protoblot System of Promega (Madison, WIS, USA) was used to visualize the recombinant protein. Rabbit-anti-prothrombin-serum (Lot No.A325) of Dakopatts (Glostrup, Denmark) was used as the antibody for prothrombin binding (Fig. 4B) Example 2: Purification and activity determination of recombinant wt-prothrombin and prothrombin derivatives a) Purification of the recombinant wt-prothrombin and of the prothrombin-Asn419 Material: Anion exchange column Fraktogel EMD TMAE 6 50, 1.6 x 5 cm (Merck) Liquid chromatography apparatus FPLC LCC-500 (Pharmacia) anti-Prothrombin-immunoglobulin (Stago) Solutions: 50 mM Tris/HCl buffer pH 7.4 (buffer A) 50 mM Tris/HCl buffer pH 7.4, 180 mM NaCl (buffer B) 50 mM Tris/HCl buffer pH 7.4, 300 mM NaCl (buffer C) 50 mM Tris/HCl buffer pH 7.4, 160 mM NaCl, 10 mM Ca-acetate (buffer D) For the recovery of the recombinant wt-prothrombin and of the prothrombin derivative, the cell culture supernatant of transformed CHO cells from Example 1 was used which contained a soluble recombinant prothrombin derivative.
Purification of the recombinant wt-prothrombin and of the prothrombin derivative from the cell culture supernatant was effected by liquid chromatography. During the chromatography, the course thereof was followed in the usual manner by absorption measurement at 280 nm. The content of prothrombin and of prothrombin derivatives, respectively, of the individual fractions and eluates was determined in the usual manner by means of ELISA by using a commercially common prothrombin preparation as the standard.

The total protein concentration was determined according to the method of Bradford, M. (Anal. Biochem. 72, 248 (1976).
The purification method is described in Fischer et al., J.
Biotechn. 38:129, 1995.
The data relating to the purification of the wt-prothrombin are not shown.
To purify prothrombin-Asn419, the anion exchange column was equilibrated with buffer A, and subsequently 970 ml of cell culture supernatant (prothrombin content (ELISA) 20 ~g/ml;
protein concentration 2.7 mg/ml) were applied at a rate of 4 ml/minute. Material not bound to the exchange gel was removed by flushing the column with buffer A ~eluate 1: 1030 ml: 1.2 mg/ml). Subsequently, proteins weakly bonded to the column were removed by flushing the column with buffer B (eluate 2: 20 ml;
prothrombin content (ELISA) 2 ~g/ml; total protein content 10.0 mg/ml). Thereafter, the column was eluted with buffer C, and protein bound to the column was obtained in the eluate (eluate 3: 30 ml; prothrombin content (ELISA) 355 ~g/ml; total protein content 16 mg/ml). Subsequently, the column was regenerated by washing with 1 M NaCl solution and equilibrated with buffer D.
28 ml of eluate 3 were 1.9-fold diluted with buffer A, and Ca-acetate was added to a final concentration of 10 mM. This solution in turn was filtered through the anion exchange column and flushed with buffer D, unbound protein being obtained in the eluate (eluate 4: 60 ml; prothrombin content (ELISA) 170 ~g/ml).
In the individual stages of chromatography, the protein was examined by means of denaturing SDS polyacrylamide gel electrophoresis (SDS-PAGE) (Laemmli, 1970). Fig. 5 shows the purification of the prothrombin derivative by means of SDS-PAGE.
From the illustration it is apparent that the prothrombin derivative in eluate 4 was obtained in pure form.
b) Activity determination of the prothrombin derivative:
All the purification stages and eluates were examined in terms of coagulation activity of prothrombin by means of prothrombin-time-test (Quick AJ, J. Biol. Chem. 109:73, 1935, and Denson KWE et al., in Laboratory Diagnosis, Blackwell R.
Scientific Publications Oxford 1976, pp. 310.) Neither in the cell culture supernatant, the individual purification stages, nor in eluates 1-4 could a prothrombin activity be detected.

Example 3: Recovery, analysis and activity determination of wt-thrombin and Thrombin-Asn99 a) Recovery of Thrombin-Asn99:
The recovery of thrombin-Asn99 was effected analogous to the method described in EP-A-0 565 512, by cleaving the prothrombin-Asn419 by means of immobilized trypsin.
The eluate obtained after activation was examined by means of denaturing SDS-PAGE (Fig. 6). The results of SDS-PAGE show that recombinant prothrombin derivative has been changed into a thrombin derivative (Thrombin-Asn99) having a molecular weight of 33,000 (heavy chain).
In parallel thereto, recombinant wt-prothrombin is activated to thrombin according to the same method.
b) Analysis of the amino acid sequence of the thrombin derivative Thrombin-Asn99 N-terminal amino acid sequence analysis yielded the following two sequences: (A) Thr-Ala-Thr-Ser-Glu-Tyr-Gln-Thr-Phe-Phe-Asn-Pro-Arg-Thr-Phe; (B) Ile-Val-Glu-Ser-Asp-Glu-Ile-Gly-Met-Ser-Pro-Trp-Gln. Thus, the sequences show that the recombinant thrombin derivative was obtained by proteolysis at the authentic cleavage sites of prothrombin (Arg271-Thr272 and Arg320-Ile321) as a two-chain molecule having ~-thrombin structure.
To better illustrate the spacial structure of the thrombin-Asn99-hirudin complex, Fig. 12 shows the molecular structure of the catalytic center. Fig. 12 shows the comparison between human thrombin and the recombinant thrombin derivative Asn99.
c) Activity determination of the recombinant Thrombin-Asn99 was effected according to three independent methods.
I. Determination of the thrombin activity by means of chromogenic substrate.
The determination of the thrombin activity by means of chromogenic substrate was effected at 25~C in 50 mM Tris/HCl buffer, 150 mM NaC1, 0.1~ PEG 6000, pH 8.0, at a concentration of the synthetic chromogenic substrate of 0.2 mM AcOH-DH-CHG-Ala-Arg-pNA (TH-1, Pentapharm) in a volume of 1 ml. The absorption at 410 nm was determined in dependence on time.
Thrombin standard of a defined activity (Immuno AG) was used as reference. The dilutions of the samples in the test buffer were effected with an addition of 1~ Prionex (collagen hydrolysate, Pentapharm).
The activity determination gave an activity of 0.24 nmol/min ~g protein for the recombinant thrombin derivative Thrombin-Asn99. Thus, Thrombin-Asn99 has an activity of merely 0.24~ in the chromogenic assay as compared to human plasmatic thrombin.

Table 1: Determination of thrombin activity by means of chromogenic substrate Thrombin Derivative Specific Activity (nmol/min ~q protein) Thrombin-Asn 99 0.24 Recombinant wt-thrombin 98.4 Human plasmatic thrombin 102.0 II. Determination of the activity by using a thrombin standard All the thrombin derivatives were assayed for their thrombin activity by using a thrombin standard (Immuno AG) of defined activity. In this activity determination, no activity was found for Thrombin-Asn99 (Table 2).

Table 2: Determination of activity by using a thrombin standard Thrombin Derivative Activity (IU/mq protein) Thrombin-Asn99 o Recombinant wt-thrombin 1656 Human plasmatic thrombin 1509.0 III. Activity determination by titration of the active site Titration of the active site of the thrombin derivatives was effected according to the method of M.F. Doyle and P.E. Haley (Methods in Enzymology (1993), 222, 299-312), by using p-nitrophenyl-p'-guanidino-benzoate as substrate and an extinction coefficient of 16,595 M~l cm~l at 410 nm.
Human plasmatic thrombin, recombinant wt-thrombin and Thrombin-Asn99 were assayed for their content at the active site (active thrombin concentration) by means of this method. With this, no active site could be found for Thrombin-Asn99 (Table 3).

Table 3: Activity determination by titration of the active site Thrombin DerivativeConcentration of Active Thrombin (nmol/mq protein) Thrombin-Asn99 0 Recombinant wt-thrombin 16.34 Human plasmatic thrombin16.89 Conclusion: In contrast to recombinant wt-thrombin and human plasmatic thrombin, Thrombin-Asn99 exhibits an extremely low thrombin activity in merely one of three test methods, corresponding to approximately 1/400 of the native thrombin activity. Recombinant wt-thrombin and human plasmatic thrombin exhibit very similar activity patterns.
Example 4: Quantitation of hirudin binding of the recombinant thrombin derivative I. The binding capacity to hirudin of the thrombin derivative Thrombin-Asn99 was examined by means of an ELISA
assay and compared with human plasmatic thrombin and recombinant wt-thrombin. This ELISA assay is based on the use of immobilized hirudin. According to one of the embodiments of this assay, thrombin is bound to hirudin which has been immobilized on microtiter plates and is detected via antibodies with subsequent colour reaction. This assay is independent of the enzymatic activity of the thrombin.
To prepare the ELISA plates, recombinant hirudin, variant 1 (Variante 1; Rhein Biotech, FRG; 2 ~g/ml, 100 ~l) is bound to microtitration plates. After washing, recombinant wt-thrombin, thrombin Asn99 or human plasmatic thrombin (100 ~l of a solution at the concentrations according to Fig. 7) is added and incubated for one hour. Non-bound thrombin was removed, and bound thrombin was detected by means of peroxidase-labelled anti-thrombin-immunoglobulin (Sheep anti-human Thrombin; Enzyme Research Lab. Inc., Indiana, USA; 100 ~l of a l/looo) (Fig. 7).

Absorption measurement was effected at 450 nm.
From the results it is clearly apparent that recombinant wt-thrombin (Fig. 7B), human plasmatic thrombin (Fig. 7C), as well as thrombin-Asn99 (Fig. 7A) bind to immobilized hirudin in identical and concentration-dependent manner.
II. Determination of the binding of hirudin to thrombin by changing the fluorescence of aromatic amino acids in the thrombin molecule and determination of the binding constant of hirudin to thrombin derivatives.
By way of fluorescence emissions, using the PC program ENZFITTER (RJ. Leatherbarrow, Elsevier-Biosoft, 1987) and by using a binding model with a mutual binding site as a basis, the binding constant of thrombin to hirudin was determined. The determination of the intrinsic fluorescence of aromatic amino acids of the thrombin derivatives was effected in 50 mM Tris/HCl buffer, 150 mM NaCl, 0.1~ PEG 6000, pH 7.4. Excitation occurred at 280 nm (gap width 2.5 nm), the emission was registered between 300 nm and 400 nm (gap width 5 nm).
The intrinsic fluorescence of tryptophane in the thrombin molecule was excited at 280 nm, and the emission between 300 nm and 400 nm was measured without the addition of hirudin and in the presence of hirudin, respectively. The fluorescence at 341 nm (excitation 280 nm) of 390 nM thrombin-Asn99, 326 nM
recombinant wt-thrombin and 350 nM human plasmatic thrombin was determined in dependence on the hirudin concentration.
Again, the thrombin derivative Thrombin-Asn99 is compared with recombinant wt-thrombin and human plasmatic thrombin. From the results it is apparent that in presence of hirudin, the fluorescence of tryptophane in the thrombin molecule (hirudin has no tryptophane) increases substantially relative to all three thrombin derivatives (Fig. 8). Apparently this is due to the formation of a hirudin-thrombin complex.
Apparently this leads to a structural change in the thrombin molecule which influences the fluorescence properties of tryptophane. From spatial structural analyses of the thrombin-hirudin complex it is known that particularly Trp 51, Trp 148 and Trp 227 from thrombin as a consequence of hirudin binding get into contact vicinity to the inhibitor.
By way of comparison, Fig. 8 shows the dependence of the thrombin fluorescence on the hirudin concentration. For all three thrombin derivatives, very similar bindings of hirudin to thrombin were obtained. The binding of hirudin to all three thrombin derivatives corresponds to a saturation and results in one binding site per thrombin molecule.
The data of Fig. 8 were used to determine the binding constants of hirudin on the thrombin derivatives (Table 4). It is apparent that very similar and very high association constants were obtained for all thrombin derivatives.

Table 4: Binding constants of hirudin to the thrombin derivatives Thrombin Derivative Association Constant of the Thrombin-Hirudin-Com~lex (M-l) Thrombin-Asn99 3.7 x 107 Recombinant wt-thrombin 4.3 x 107 Human plasmatic thrombin 3.2 x 107 Example 5: Recombinant prothrombin as hirudin-antagonist Material: Coagulometer KC 10 (Amelungen GmbH, Germany) Prothrombin-free normal plasma (Immuno AG, Vienna) Prothrombin concentration standard (Immuno AG, Vienna) Recombinant hirudin (Rhein Biotech, Germany) In a common laboratory method, the time required after activation of the factors participating in blood coagulation to make normal plasma coagulate was determined by means of a prothrombin-time-assay. By the addition of Ca2+ ions to the mixture of 1. prothrombin-free normal plasma (which, however, contains all the other coagulation factors), and 2. prothrombin concentration standard (prothrombin having a defined activity), in this assay coagulation factor Xa is formed which then converts prothrombin (factor II) into thrombin (factor IIa).
Thrombin then causes the conversion of soluble fibrinogen into insoluble fibrin. This leads to the formation of blood clots.
The time interval between activation by the addition of the Ca2+
ions and the formation of the blood clot is automatically determined by means of the coagulometer. As is known, the duration of blood coagulation depends on the concentration of .

the prothrombin or on the concentration of the active thrombin formed, respectively. The higher the thrombin concentration in the reaction mixture, the lower the clotting time. With the addition of a thrombin inhibitor, such as hirudin, an inactive thrombin-hirudin complex forms after the conversion of prothrombin to thrombin, so that in thrombin bound in this complex can no longer participate in the conversion of fibrinogen to fibrin. As a consequence, the clotting time increases on account of the reduced amount of active thrombin.
With an excess of inhibitor as compared to thrombin, there results a complete inhibition of blood coagulation. If however, both, a thrombin inhibitor, such as hirudin, and a further component which in turn binds the inhibitor but does not participate in blood coagulation are added in an assay system, the effect of the inhibitor on thrombin decreases. Then the clotting time is shortened again. In Table 5, the results of various ex~m~n~tions are summarized:
From the results of Table 5 there follows:
1. Prothrombin leads to a rapid formation of the blood clot.
2. Hirudin leads to an inhibition of blood coagulation.
3. The recombinant prothrombin derivative does not lead to blood coagulation.
4. The recombinant prothrombin derivative does not affect the blood coagulation by natural prothrombin.

5. By the addition of recombinant prothrombin derivative, the hirudin-dependent inhibition of blood coagulation is cancelled out.

CA 02224634 l997-l2-l2 Table 5:

Components in the Coaqulation Assay Clotting Time (s) Formulation (A) Prothrombin-free normal plasma 125 mU/ml (12.5 ~g/ml) prothrombin 18 Formulation (B) Prothrombin-free normal plasma 125 mU/ml (12.5 ~g/ml) prothrombin 2.5 ~g/ml hirudin > 100 Formulation (C) Prothrombin-free normal plasma 25 ~g/ml prothrombin derivative according to the invention > 100 Formulation (D) Prothrombin-free normal plasma 125 mU/ml (12.5 llg/ml) prothrombin 25 ~g/ml prothrombin derivative according to the invention 18 Formulation (E) Prothrombin-free normal plasma 125 mU/ml (12.5 ~g/ml) prothrombin 25 ~g/ml prothrombin derivative accordinq to the invention, 2.5 ~q/ml hirudin 35 Example 6: Neutralization of hirudin by Thrombin-Asn99 To test whether or not Thrombin-Asn99 is able to neutralize hirudin and thus the inhibition relative to active thrombin is cancelled out, 50 ~1l of hirudin (44 nM, 4 ATU/ml) having various concentrations of thrombin-Asn99 were incubated for 1 minute.
Subsequently, 50 ~1l of thrombin standard (3.9 IU/ml) as well as a chromogenic substrate were added in measuring buffer (0. 2 mM
substrate according to Example 3C in 50 mM Tris/HCl buffer, 150 mM NaC1, 0.1~ PEG 6000, pH 8.0), and the enzymatic activity was determined at 25~C. The thrombin activity was photometrical-ly determined at 410 nm. For reasons of comparison, the thrombin activity without hirudin (100~ thrombin activity), as well as the thrombin activity in the presence of hirudin, yet without the addition of Thrombin-Asn99 (0~ thrombin activity) were determined. The results are illustrated in Fig. 9 It is clearly apparent that hirudin is neutralized by Thrombin-Asn99, and thus the inhibiting effect of hirudin on active thrombin is cancelled out. Simultaneously it becomes clear that at a ratio of 1 mol Thrombin-Asn99 to 1 mol hirudin, the thrombin inhibition is neutralized.
Example 7: Reactivation of the thrombin-hirudin complex by Thrombin-Asn99 The experiment was aimed at determining whether or not the thrombin activity can be re-attained by the addition of Thrombin-Asn99 to the thrombin-hirudin complex, i.e. whether or not Thrombin-Asn99 is capable of neutralizing hirudin from the thrombin-hirudin complex.
For this, the activity of thrombin (final concentration 0.1 IU/ml) was continuously photometrically determined by means of chromogenic substrate. After 3 minutes, hirudin (final concentration 0.1 ATU/ml) was added, and the reaction was continued for further 4 minutes. Then different concentrations of Thrombin-Asn99 (final concentrations 0.2 ~g/ml, 0.4 ~g/ml and 1 ~g/ml) were added, and the reaction was followed photometrically (Fig. 7).
Fig. 10 shows that by the addition of hirudin to thrombin, the activity of the latter is inhibited. From the results it is furthermore apparent that by the addition of increasing concentrations of thrombin-Asn 99, it is, however, possible to cancel out again the inhibitory action of hirudin on thrombin.
What is interesting is that the process of hirudin neutralization is time-dependent; it takes approximately 1 minute for hirudin to become neutralized by Thrombin-Asn99. This is due to the very high binding constant of hirudin to thrombin, whose balance consequently is shifted time-dependent in favour of free thrombin and the formation of a hirudin-Thrombin-Asn99 complex.

Example 8: Neutralization of hirudin in plasma The examination was aimed at showing that Thrombin-Asn99 is capable of neutralizing hirudin in plasma, too, and thus of cancelling out an inhibiting effect of hirudin on thrombin. For the realization thereof, analogous to the aPPT-test, 110 ~l of hirudinized citrated plasma (hirudin concentration 1.8 ~g/ml) were mixed with 100 ~l of partial thromboplastin reagent (Boehringer Mannheim, FRG) and 10~1 of Thrombin-Asn99 (from 0 -17 ~g/ml according to Fig. 11) and incubated for 3 minutes at 37~C. Subsequently, 100 ~l 25 mM CaCl2 were added, and the clotting time was determined automatically (Fig. 11).
From the results it is apparent that the clotting time is greatly increased by hirudin (without the addition of Thrombin-Asn99). Depending on the concentration, the clotting time decreases, however, with an increasing amount of Thrombin-Asn99 and reaches the values common for normal plasma.
From the illustration it appears clearly that hirudin is neutralized by Thrombin-Asn99 also in plasma, and thus the inhibition of hirudin on plasmatic thrombin is cancelled out.
In sum, the examination results show unambiguously that the thrombin mutant prepared, Thrombin-Asn99, according to the set aim merely has a negligibly low activity (less than 0.24~ of active thrombin), but binds hirudin in an identical manner.
The property of binding hirudin enables the recombinant molecule to neutralize the inhibitor both, in the defined buffer system and in plasma. Moreover, Thrombin-Asn99 is capable of displacing hirudin from the thrombin-hirudin complex and to neutralize it.
Example 9: Recovery and functional analysis of meizothrombin-Asn419 Prothrombin-Asn 419 of Example 1 was used for the recovery of recombinant meizothrombin-Asn419. Prothrombin-Asn419 was converted to meizothrombin-Asn419 by incubation with the venom-protease ecarin. There, prothrombin-Asn419 at 0.2 mg/ml in 20 mM
Tris/HCl buffer, pH 7.4, 150 mM NaCl, 5 mM CaCl2, was dissolved and 20 ng of ecarin (product of Pentapharm) were added to each 1 ~g prothrombin-Asn419. Activation was effected at 4~C for 4 hours. The resultant meizothrombin-Asn419 was purified and isolated analogous to the purification of Thrombin-Asn99 (Example 3) by affinity chromatography on the peptide-gel.
Meizothrombin-Asn419 prepared in this manner has the identical molecular weight of Prothrombin-Asn419 of 72,000 and consists of the Prothrombin-F1/F2/A chain (molecular weight 52,000, N-terminal amino acid sequence Ala-Asn-Thr-Phe-Leu-Gla-Gla-) and the B-chain (molecular weight 32,000, N-terminal amino acid sequence Ile-Val-Glu-Ser-Asp-Ala-Glu-Ile).
Analogous to the Examples 3 (c) I to III, the enzymatic properties of Meizothrombin-Asn419 were assayed. In none of the test methods an activity was determined for Meizothrombin-Asn419.
Analogous to Example 4 (I) and (II) it could be found out that Meizothrombin-Asn419 binds to immobilized hirudin in a concentration-dependent manner and with a strength comparable to human plasmatic thrombin and that the fluorescence intensity of aromatic amino acids increases by the binding to hirudin, as described for Thrombin-Asn99.
Analogous to Example 6 it could be demonstrated for Meizothrombin-Asn419 that it neutralizes hirudin and thus cancels out the inhibition relative to thrombin. At a ratio of 1 mol of Meizothrombin-Asn419 to 1 mol of hirudin, the thrombin inhibition is neutralized.
Analogous to Example 7, it could be demonstrated for Meizothrombin-Asn419 that hirudin can be displaced again from the complex by the addition of Meizothrombin-Asn419 to the thrombin-hirudin-complex, and thus the thrombin recovers its acitivity. The data obtained therein correspond to those of Thrombin-Asn99.
Analogous to Example 8 it could be demonstrated for Meizothrombin-Asn419 that it is capable to neutralize hirudin in plasma and thus cancel out the inhibitory action of thrombin.
The data obtained therein correspond to those of Thrombin-Asn99.
Example 10: Characterization of Thrombin-Asn99 and Meizothrombin-Asn99 in vivo The hirudin-neutralizing effects of Thrombin-Asn99 and Meizothrombin-Asn99 were assayed in an animal model: 3 min after an intravenous administration of a hirudin dose of 0.5 mg per kg body weight (200 ~l) or of 200 ~l of saline solution to NMRI
mice (20 g body weight; each test group comprised 10 mice), 2.5 mg of Thrombin-Asn99/kg body weight and 5.0 mg of Meizothrombin-Asn99 (200 ~l each) were injected. After further 3 minutes, blood was taken from the anaesthesized mice by cardiopuncture. The citrated plasma obtained was assayed for partial thromboplastin time (PTT), thrombin time (TT), anti-thrombin potential (aPT) and plasma concentration of Thrombin-Asn99 and Meizothrombin-Asn99, each measurement being carried out in triplicate.
To measure the PTT, 50 ~l of citrated mouse plasma were mixed with 50 ~l of factor II-deficient citrated plasma and 100 ~l of partial thromboplastin reagent at 37~C for 3 minutes.
Coagulation was started by the addition of 100 ~l 25 mM CaCl2.
To measure the TT, 50 ~l of citrated mouse plasma were mixed with 150 ~l of factor II-deficient citrated plasma at 37~C for 1 minute. Coagulation was started by the addition of 100 ~l of thrombin-standard (7 units/ml).
To determine the aPT, the TT of all mice of groups 1 to 8 were compared with a calibration curve of the clotting times of various thrombin standard concentrations (1 unit/ml to 10 units/ml), from which there resulted the effective thrombin concentration in the individual TT tests. The resulting differences in the effective thrombin concentration in the tests with the mouse plasma of test groups 1 and 5 to the effective thrombin concentrations in the tests with the mouse plasma of test groups 2 to 4 and 6 to 8, respectively, resulted in the anti-thrombin potential, a difference in 1 thrombin unit/ml being defined as one anti-thrombin unit.
The plasma concentrations of Thrombin-Asn99 and Meizothrombin-Asn 99 were determined by the addition of serial plasma dilutions to immobilized hirudin, Thrombin-Asn99 and Meizothrombin-Asn99 being detected by means of sheep-anti-thrombin-IgG-peroxidase conjugate. For an analysis, calibration straight lines were established by means of Thrombin-Asn99 and Meizothrombin-Asn99 concentrations of 3 ng/ml to 100 ng/ml.
The results of these assays are illustrated in Table 6.

Table 6:

ParameterThrombin-Asn99 Meizothrombin-Asn99 Test Group Test Group PTT (sec) 23.8 42.3 24.0 26.2 22.4 38.2 21.0 21.8 TT (sec) 11.4 19.8 11.6 11.7 11.6 19.3 11.2 12.0 aTP (ATU) 0 4.3 0 0.33 0 3.8 0 0.12 Plasma con-centration 0 0 16 10 0 0 39 16 These data illustrate that the injection of hirudin (test groups 2 and 6) caused an increase of the PTT of at least 75~, and increase of the TT of at least 60~, the occurrence of a high aPT and no detection of thrombin in plasma.
The sole administration of Thrombin-Asn99 (test group 3) and Meizothrombin-Asn99 (test group 7) did not show any significant change of the coagulation parameters, when compared with the test groups 1 and 5, respectively, yet both proteins could be detected in mouse plasma.
The injection of hirudin followed by Thrombin-Asn99 (test group 4), and the injection of hirudin followed by Meizothrombin-Asn99 (test group 8) resulted in a normalization of the PTT and the TT, the aPT being markedly reduced. Thus, both proteins apparently were able to neutralize hirudin in circulation and thus reduce the free hirudin concentration.
Hirudin-complexed forms of Thrombin-Asn99 and Meizothrombin-Asn99 are less reactive relative to immobilized hirudin, and therefore lower concentrations of Thrombin-Asn99 and Meizothrombin-Asn99 were found in the plasma.

Claims (15)

Claims:

1. A prothrombin mutant or derivative thereof, characterized in that it comprises an exchange of the amino acid Asp-419, based on the amino acid numbering in prothrombin according to Fig. 1, an activity of approximately 0.25% at the most of the natural protein, and in which the change of the protein sequence does not affect its binding capacity to hirudin, heparin and antithrombin III.

2. A prothrombin mutant or derivative thereof according to claim 1, characterized in that it has an in vivo half-life of more than one hour.

3. A prothrombin mutant or derivative thereof according to claim 1, characterized in that it has an in vivo half-life of 10 minutes at the most.

4. A prothrombin mutant or derivative thereof according to any one of claims 1 to 3, characterized in that the amino acid Asp-419 has been exchanged for Asn.

5. A prothrombin mutant or derivative thereof according to any one of claims 1 to 4, characterized in that it comprises an amino acid exchange of Cys-293 and/or Cys-439, based on the amino acid numbering in prothrombin according to Fig. 1.

6. A meizothrombin mutant, characterized in that it is structurally stable, comprises at least one amino acid exchange at the active site, has an activity of approximately 0.25% at the most of the natural protein, and in which the change of the protein sequence does not affect its binding capacity to specific ligands and receptors.

7. A meizothrombin mutant according to claim 6, characterized in that it comprises an amino acid exchange of Cys-293 and/or Cys-439, based on the amino acid numbering in prothrombin according to Fig. 1.

8. A meizothrombin mutant according to claim 6 or 7, characterized in that the amino acid Asp-419 has been exchanged for Asn.

9. A pharmaceutical preparation containing a prothrombin mutant or a derivative thereof comprising an exchange of the amino acid Asp-419, based on the amino acid numbering in prothrombin according to Fig. 1, an activity of approximately 0.25% at the most of the natural protein, and in which the change of the protein sequence does not affect its binding capacity to hirudin, heparin and antithrombin III, and a physiologically acceptable carrier.

10. A pharmaceutical preparation according to claim 9, characterized in that the prothrombin mutant or a derivative thereof comprises an amino acid exchange of Cys-293 and/or Cys-439, based on the amino acid numbering in prothrombin according to Fig. 1.

11. A pharmaceutical preparation according to claim 9 or 10, characterized in that it is substantially free from viral contaminations and impurities by residual-DNA from the expression cell line.

12. The use of a prothrombin mutant or derivative thereof which comprises an exchange of the amino acid Asp-419, based on the amino acid numbering in prothrombin according to Fig. 1, an activity of approximately 0.25% at the most of the natural protein, and in which the change of the protein sequence substantially does not affect its binding capacity to hirudin, heparin and antithrombin III, for preparing a medicament for preventing the side effects associated with an anticoagulation treatment with hirudin, heparin, antithrombin III and/or derivatives thereof.

13. The use according to claim 12, characterized in that the prothrombin mutant comprises an amino acid exchange of Cys-293 and/or Cys-439, based on the amino acid numbering in prothrombin according to Fig. 1.

14. The use of a prothrombin mutant or derivative thereof which comprises an exchange of amino acid Asp-419, based on the amino acid numbering in prothrombin according to Fig. 1, an activity of approximately 0.25% at the most of the natural protein, and in which the change of the protein sequence substantially does not affect its binding capacity to hirudin, heparin and antithrombin III, for producing a preparation which exhibits an antagonistic action relative to a natural or synthetic thrombin inhibitor, in particular to hirudin, heparin, antithrombin III and/or derivatives thereof.

15. The use according to claim 14, characterized in that the prothrombin mutant comprises an amino acid exchange of Cys-293 and/or Cys-439, based on the amino acid numbering in prothrombin according to Fig. 1.